1. Field of the Invention
The present invention relates to a semiconductor device comprising in its composition a thin film transistor (hereinafter, referred to as TFT) that uses a semiconductor thin film, and to a method of manufacturing the same. In this specification, the term “semiconductor device” denotes devices in general which may function with utilization of semiconductor characteristics, and hence semiconductor circuits, electro-optical devices and electronic equipments in this specification all fall into the semiconductor device.
2. Description of the Related Art
In recent years, what have attracted attention is an active matrix type liquid crystal display device including a circuit constituted of a TFT that uses a polysilicon film. The device is designed to control on matrix-basis, by means of a plurality of pixels arranged in matrix, the electric field that is applied onto liquid crystal, thereby realizing image display of high definition.
In an active matrix type liquid crystal display device, an image is displayed by controlling with a pixel TFT formed for every pixel the voltage applied to liquid crystal. Today's display device has a million or more pixels besides many other components, so that huge numbers of pixel TFTs have to be formed with good yield while holding down the variation in their characteristics.
The interface between an active layer and a gate insulating film may be given as one of parameters that influence the TFT characteristics most. When contaminated, this interface affects in an instant the TFT characteristics. Purifying the interface at which the active layer and other insulating film are brought into contact is therefore necessary to obtain good TFT characteristics.